Process and apparatus for dewaxing oils



Nov. 10, 1936. D. R. MERRILL I PROCESS AND APPARATUS FOR DEWAXING OILS 4 2 Sheets-Sheet 1 Filed May 22, 1934 EN W NE INVENTQR. Dawn. 1?. Merrzll MW 9 Q ATTORNEY.

Nov. 10, 1936.

D. R. MERRILL PROCESS AND APPARATUS FOR DEWAXING OILS Filed May 22, 1934 2 Sheets-Shea 2- k '0? 5 u I" N 0 h ll' 0 II N' N '8 L. a; m g E 3 n 3 E 9,. Q

g H INVENTOR 0 David RMerrzlZ 'Q BY 1 Em ,gk ATTORNEY. I

. Patented Nov. 10,1936 a I 2,060,517

UNITED STATES PATENT OFFICE rnocliss AND APPARATUS FOR a DEWAXINGCILS David a; Merrill, Long Beach, Califgassignor to' Union Oil Company of California, Los Angelcs, Calif a corporation of California Application May 22, 1934, Serial No.- 726;969 23 Claims. (cl. 02-170) The present invention relates to aprocess and formation or new nuclei will occur to only a very apparatus forseparating wax from mineral oils limited extent, if at all. This range of supersuch as from petroleum, its residues or overhead saturation is commonly referred to as the metafractions and, from wax-containing lubricating stable range. For purposes of definition. the

011 stocks for the production of lubricatingoils metastable range of supersaturation is that range 5; of low pour point. The invention more particuof supersaturation within which crystallization larly relates to a process and apparatus for chilloccurs onthe surfaces of crystals already presingo wax-containing oils in order to obtain a out and spontaneous formation of new crystal controlled precipitation of the wax from .the nuclei in large amount does not occur. wax-containing stocks. As soon'as the metastable range of supersatu 10 In lubricating stocks, especially those 0! conration is exceeded, however, a so-called labile siderable viscosity range or boiling range, there range of supersaturation is reached in which will normally be present waxes varying widely rapid formation of new crystal nucleiwill occur. in characteristics comprising at the one extreme, Thus, the labllerange of supersaturation denotes 5 hard waxes of relatively high melting point, such a degree of supersaturation in which spontane- 1 as, for example, 150 F, and at the other 'exous formation of new crystal nuclei occurs to a treme, soft waxes of relatively low melting point, very large extent. With a slow rate of chilling, such as, for example, 110 F. Although ordithe'rate .0! erystalliza l n p n the W x l i narily only a small proportion of the total wax already present is sufiiciently rapid to relieve the content in the lubricating 011 stock will consist supersaturation and permit crystallization to 00- 20 of hard waxes, their presence in the waxy stock cur within the metastable range so that 11110011- ls very important since they have such a low soltrolled formation of new nuclei .does not occur. ubility in the solutionof waxy oil and diluent and With an excessively,rapid rate of chilling, how'- are usually the flrst'type of wax to separate on ever. the des e of supersaturation exceeds the gra' ual cooling. Also because of the .lowinitial metastable range and this results in the forma} 25 concentration in the solution such hard'waxes 1 1 11 of a s n mb rs 01' new nu lei and sens are precipitated in a'very finely divided form on quent reduction in the average particle size due excessively rapid chilling and also because of to the'production of a large amount of fine par.- their low solubility show little tendency towards 'ticles which are, of a gelatinous or slimy charresolution of these fine particles and crystal acte'lf. A waxslurry of this character is diilicult 30 growth. It is, therefore, evident that the most to separate from the oil solvent solution .by either critical temperature range is that in whichthe t ni; or filtering. The p rmis i l a initial separation of wax occurs because if an ch lling will. of c urs depend .not nly n t excessive number of nuclei are formed at this ent 1 t metastable nge but also up n the time there is little possibility of correcting this, rate atvwhich supersat r ion is rel v y 35 situation by subsequent digesting operations. It a lization upon particles of wax already Dr entis an object of my invention to control the fort is ano object of my invention to control mation of nucleiduring the initial stages of wax n i io and ra e 01' hilling in dewaxing 0P- separation so as to prevent formation of an exr fl Wi hin h m le r n f p 40 cessive number of such nuclei'and to permit furststuration d to ie pe sa ura ion by .0 ther crystal growth on nuclei formed in the early c ys all zation of wax on wax partic es r ady stages or chilling. ,present in thesolution. I

In general, crystallization of wax is accom- In one known methods for separating plished by inducing a supersaturated condition was from oila'the o l s 'e w h a hydrocarbon in the solution of waxy oil and solvent employed solvent, morelparticularly a liquefied normally 4 to dilute the oil. This is accomplished either by. gaseous hydrocarbon solvent, such as liqui D increasing the concentration of the solute by --'mne- The a x r is effected un r a Dr vaporization or separation-of solvent, or by r'e-j' sure sufiicient-to maintain the solvent in the ducing the solubility by cooling, orboth. some liquid phase he ea r. abo t on of the solinvestigators, have shown there is a narrow range vent is vaporized under reduced pressure in order 50 of concentration and a corresponding range oi to effect chilling and precipitation of waxfrom temperature of supersaturation within which solution. In the case of propane, by reducin free formation of new crystal nuclei will not the pressure down to atmospheric, a temperaturg occur. In this range of. supersaturation, crystaloiapproximately -40 F. may be obtained in the lization will'occur onnuclei already present but remaining oil and solvent solution. The wax 4 5 4 maintain a sufilcient volume of liquid in the tower,

the rate of. cooling of the stream can be readily 'controlled. Due to the relatively low specific gravity of the propane solution, the height of the tower required will be about 4 ft. for each pound drop in pressure. The number of towers and of stages shown-in each tower is merely by way of illustration and in practice considerably more stages would be desirable, as except for eddy currents in the passage past the vapor collecting chambers some fall in temperature will tend to Upon reaching .thetop of the first chiller the I solution flows down through line 30 and valve 31 which is actuated by a float control 30 in the first chamber. It wilrbe noted that this valve is located at a low'levelso that the pressure on the down stream side of the valve will not be less than the vapor pressure of the solution as would be the case if it were located at the ,high' level. In this way flashing upon passage through the valve is avoided. The pressure at the bottom of the second column 23a made up of the sum of pressure vapor at the top and the hydrostatic head is preferably maintained exactly the same a as the pressure at the top of the first column so that there will be no flashing of the entering stream and the chilling may continue at a uniform rate. The flow of liquid through the second'column 23a and .subsequent'columns 23b and Be and the remove! of 1 vaporized A "propane is accomplished in exactly the same ,man-

ner as in the first column 23. The pressure'at the top of columns 23a, 23b, and 2 3c'is controlled by compressors a; 35b and 35c. .It is apparent that the number of columns pmvided should besufiicient so that the chilled solution leaving the top of the last column will-be at the desired dewaxing temperature'as, for example, 40 F. If desired,

after a temperature of about 0 F. is reached and most of the wax is precipitated, further chilling may be carried out at a more rapid rate or even by a flashing operation with only moderate deterioratlon'in the filtration or settling characteristics of the wax slurry. The chilling in the range from 0 F. to the final temperature of -40 F. may also be accomplished by mixing with a recirculated stream of chilled. mixture at +40 F. If the wax is of such character that deleterious quantities of particles would not be formed, a simple flashing operation may be carried out to chill the oil from about 0 F. down to '40 F. Where the oil being chilled does not contain suflicient propane .to accomplish the desired chilling. urther quantities may be introduced through lines 42 contfolled byvalves 43.

' In ,order to avoid excessive height of-equip- I ment, the chiller'is' preferably made up of a numessential. The pressure and temperature condiber ofstages or towers'as shown but this is not tions at the bottom of the second tower, for example, are preferably maintained exactly the same as at the top of the first ,tower and this relation is maintained in the subsequent stages so that in eiteot the diflerent stages represent continuously hanging conditions in the stream. For example, when it is desired to chill the oilpropanesoliition from 90 Etc -40 F. the oil-- propane solution in line II at a temperature of 90F. and under a pressureof 153 1b.,gauge is introduced into the bottom of the first chiller 23 under the aforesaid conditions. In rising in the li tower the solution is cooled by vaporization of propane at each of the stages due to the lessening of the hydrostatic head. If the chilling system is divided into four towers as shown in the drawings, the vapor pressure at the top of first 10 tower is maintained at about 111 lb. g auge by compressor 35 which corresponds to about 70 F. The oil and propane at the top of tower 23 is introduced into the bottom or the second tower 2311 under the same pressure and temperature 15 conditions existing at the top of the preceding tower. In tower23a, vaporization of propane cools the'stream to approxirntely 42 F. when it reaches the top of the tower. A pressure of about 69 lb. gauge is maintained at the top by com- 2 pressor 35a. The oil and propane .under the same temperature and pressure conditions at the top of tower 23a is introduced into tower 23b in whichit is cooled to 0 F. as it rises to the top of the tower; A pressure of about 27 lb. gauge is maintained at the top of the tower by compressor 23b. The chilled oil and propane is next intro- ;duced into the bottom of thelast chilling stage 230 at 0 F. in which it is chilled to --40 F. by

vaporization of propane as it reaches the top of 30 tower 23c. A pressure of 0 lb. gauge is'maintained at the top of the tower by compressor 230. Although in the drawings, a float control is shown onthe vapor leaving the top of the column,'.i t should be understood that this is only a safetyprebaution as the level at this point will normally be controlled by the flow of liquid to the next stage. The float control ac uating the valve on the vapor line will preferably be so adjusted as to close this valve only if an abnormally high 4 liquid. level is reached.

The propane vapors separated from.the various towers passing into headers 03 and to compressors 35, 35a, 35b, and 35c pass into header 38 and then through line 3.9 to cooler 40 where the compressed vapors are liquefied and then pass via line 41 into propane storage tank 8.- Although in the drawings the valves '32 are shown all connected to the same headers, in

practice it is often more desirable to have several headers operating at different pressures so as to reduce the power required for compression by avoid ing unnecessary expansion and recompression.

.The chilled oil and remaining propane solution containing precipitated wax preferably in the ratio of approximately 3 to 4 volumes of propane to one of the oil and wax is withdrawn from the top of the last chilling tower 230 at a temperature of -40 FQ via line, 45 by means of pump 40 which forces the mixture into the vapor 00 tight wax separatoror settler 47. Make-up propane at -40 F. may be introduced into the chilled 011 via line 44 controlled by valve 44, in order to provide for adequate settling or filtration of the precipitated Max. In order to prevent ebullition or boiling in the wax separator duringthe wax settling operation. pressure is imposed upon the solution of oil. This is accomplished by maintaining pressure within the separator by pump 46. As the chilled mass in the wax separator remains in a non-ebullient state) the wax setties out and is collected by vanes 48. on shaft 40 which is operated-by belt 50 connected to a suit,- able source of power not shown.; The wax-free oil dissolved in propane is withdrawn from the 76 separator 4! via line 5| and is passedinto collecting tank 52.

The precipitated wax slurry containing propane settling at the bottom 01' the wax separator 5 41' is removed through line 53 and pumped by pump 54 into line 55 where it meets'a stream of chilled recovered oil and propane from surge tank 58 via', line 51 and pump 58. The two streams then pass through line 55 and mixer 58 into settler 88 which is constructed in a manner similar. to settler 41 and in which the wax fromsettler 4-1 washed with the dilute oil propane solution fromsurge tank 58. Oil and propane separated from the wax slurry is'withdrawn via line 6| and .passed into collecting tank 52. The

oncewashed wax slurry is withdrawn from the bottom of settler 88 'viailine 62 and pump 83 which forces the wax slurry through line 64 wherein it meets a stream of chilled propane at 88--40 F. coming from chilled propane storage tank 85 via line 66, pump 61, line -68 and. valve 88; The mixture then flows through mixing coil 18 into another settler II constructed'similarly v to settlers 41 and 88. In settler II the wax from settler 88 is washed with the fresh chilled propane and any oil separated-is withdrawn together with the chilled propane via line I2 and passed into surge tank 56. As stated previously, this solution containing a small amount of recovered I! oil is employed to wash the wax slurry from the first settler 41. The countercurrcnt washing .steps may be carried on in as many stages as desired. The chilled propane in tank 65 is produced by withdrawing a portion of the propane under pressure from tank 8 via lines 9 and I5, cooling it in heat interchangers I8 and I1 and passing it into tank 85. The propane in 85 is chilled to .F. by vaporizing a portionthrough line I8 and compressor I8 which forces 0 the vaporized propane through lines 88, 8| and 38, cooler 48, line H intopropane storage tankjl The substantially oil-free wax is withdrawn from the bottom of settler 1| vialine 82 and pump 83 which forces the-wax through line 84,

heat interchanger 85, line 88 into high pressure exhauster 81 where vaporized propane under high pressure is withdrawn via line 88 into line 89.. -Wax in exhauster 81 is continuously recirculated from the bottom into the top of the exhauster via line 88, pump 8|, line 82, heater 83 and line 84. The wax, or a portion thereof, is then passed through valve 85, line 86, heater 81, line 88 into the low pressure exhauster 88. Vaporized propane under low pressure is withdrawn via line I88, compressed in compressor IM and passed into line 88. Wax-in low pressure exhauster 88 is recirculated via line- I82, pump I83, valve I84, line 88,- heater 81 and line 88. Substantially "propane-iree-wax is withdrawn through valve 88 'I85' and passed through cooler I86, line I81 into 7 wax storage'tank I88 where it ismaintained,

melted by steam circulated through coil I88.

The substantially wax-free oil and propane from collecting tank 52 is withdrawn via line I I8 55 and pumped by pump III through line II2, heat interch'ange'r' II4, line II5, yalve IIBinto high pressure exhauster II I where vaporized propane -under high pressure is withdrawn via line H8. The oil in high pressure-exhauSter III is con- 10 tinuously' recirculated through line II8, pum I28, line I2I, heater I22 and line I23. The of.

containing the remaining propane is then passed I28, line I21 through valve I24, line 125, heater into'l ow pressureexhauster J28. Propaneand 7 oil from thelowpressureexhausteria continuously recirculated through line I 28, pump I38,-valve I3I, line I25, heater I28; line I2'I into exhauster I28. -Vaporized propane under low pressure is withdrawn from low pressure exhauster via line A I32 and passed into line I88, compressed in I8I lines I31, 8i and 38, cooler -48, line 4I into propane storage tank 8.

In the foregoing disclosure Ihave described a method for utilizing hydrostatic pressure of the propane oil solution for controlling the pressure at various points in a continuous chilling system in which propane is employed as an internal refrigerant. In the system just described; float valves are employed for controlling the flow of vapor from each stage of vapor evolution. In the equipment shown in the drawings, a number of stages are placed one above the other in a column for convenience of construction but this, of course, is not essential and each stage may be constructed separately, if desired. In the following description of Figs. 2, 3, and 4 I have illustrated other methods of control whileretaining the'use of hydrostatic head as a means of establishing pressure differentials between stages. It

will be observed that Figs. 2, 3, and 4 merely.

show aseries of chilling chambers. However, it will be understood that apparatus for mixing propane and waxy oil and for preparing the mix- .ture prior to introduction into the chilling chamhers is similar to that described in Fig. 1. Likewise, the-apparatus for separating the precipitated wax from the'oil and propane and ior separating propane from the separated oil and wax fractions and for recovering propane may be carried on similarly to that described for Fig. 1.

In Fig. 2 I have shown asimplifled form for chilling the oil and propane solution by which float valves are employed for controlling the evolution of vapors from each stage. In this figure, the mixture of-oil and propane containing wax is introduced into the bottom of the first chill chamber 23 via line 2I and as it rises in the column the hydrostatic head becomes less and propane is vaporized which is withdrawn from the top via line 3| controlled by valve 32 which chiller 23a. by means of float control 38. The propane and oil from the first stage 23' flows into the second stage 23a via conduit 35, which is of sufiiclent size so that the flowing stream is controlled by the level of liquid in the second' willnot fill it completely and interfere with pressure equalization between the top of chiller 23 and the bottom chamber of chiller 230 for example. Likewise, the flow fromjthe second chilling column 280 into 'the third chilling column 23b and from 231) to 280 is accomplished in the same manner. The propane, and oil solution from chiller 23c then overflows into an accumulating chamber 24 where the cold mixture is accumulated and drawn oil as required to the filters or settlers. The last" chiller and the accumulator will normally be maintained at the same pressure and temperature. The chilled solution carrying A precipitated wax is withdrawn from the bottom I of chamber 24 via line 45 and passed to settlers propane. The vaporized propane or filters or other means for separating-the pre-- v cipitated wax from the chilled oiland remaining man each chill- 1 each stage.

For convenience, the conduits connecting one stage with the next are made sufllciently large so that counterflow of liquid 'and vapor may occur without surging and thus a single vapor take.-

oii' from the top of the stage is sufficient rather than vapor take-oil's from both the top and the float control chamber.

Instead ,oi! employing float. control valves, I

may employ pressure control valves as shown in Figs. 8 and 4. In Fig. 3, pressure control valves 82 are employed on the vapors leaving each stage which valves are so set as to establish a definite pressure in each stage different from thatfor the adjacent stage by a definite amount. These valves are of the pressure relief type which will release whenthe pressure on the up-stream side of the valve exceeds the setting and will close when the pressure falls below the setting point. Through the controlled release of vapor from each stage, definite pressures will beestablished corresponding with definite temperatures varying in the desired manner from stage to stage. By accurate control of the difference in pressure between'stages, this difference will be maintained at a value which can properly be balanced by the hydrostatic head capable of being established by the difference in the level in the stage itself and the transfer conduit leading to the stage.

Since the proper establishment of such hydrostatic headrequires the use of pressure control valves of relatively high precision of operation, it may be more desirable in some cases to employ a difierential pressure control valve according to the method illustrated in Fig. 4. Examples of suitable valves for this use are valves 32 operated by diaphragms 32a in which pressure can be applied to both sides of the diaphragm. The difierential force generated by variation in pressure on two sides of the diaphragm is ordinarily balanced by a spring under adjustable tension so that the valve will open when the diflerential is too high and close when the difi'erential is too low. Thus,

when the difierential between stages tends to become too high so that there is danger of-the liquid in the trap being blown out by the vapor, the resfiective valve 32 1 open and will release vapor until a suitable pressure diflerentialis reestablished. -By proper adjustment of the valves pressure differentials between stages can be established which will permit efllcient utilization of the available hydrostatic head.

In starting such equipment, it will usually be found desirable to fill all the stages with either the oil solution in propane or propane. at the usual feed temperature and then to release 'propane vapor from the last stageat such a rate as to give a ,suitable chilling rate such as not to exceed 2 or 3 F. per minute. As the-vapor is evolved in the last stage, the temperature and pressure in this stage will fall and upbn establishment of the desired differential pressure be- .tween this stage and. the immediately preceding stage, the diaphragm of the valve on the preceding stage is actuated so that v'apor begins to fipw from this stage and cooling of the solution in this stage starts. This operation is repeated.

until'ffinally the des ired temperature isTreached chambers by lessening of .trol the liquid in the last stage and the vapor outlet valves on all the stages, except possibly a few surplus stages at the beginning are in operation. Although in the drawings, these valves are shown, all connected to the same header, in practice it is more C desirable to have several headers operating at difierent pressures so as to reduce the power re-v quired for compression by avoiding unnecessary expansion and recompression..

While I have described the use of liquid propane as the internal refrigerant-diluent, it will be observed that I may employ other liquefied normally gaseous hydrocarbons'for this purpose.

Such hydrocarbons include methane, ethane, propane, iso-butane, butane or'mixt'ures thereof. These hydrocarbons may be obtained by rectification of casinghead gasoline by the so-called stabilizing method. They are the overhead thus obtained. They are liquefied by compression and cooling in the conventional manner and are drawn off into pressure chambers .where they are maintained in the liquid state until they are used. It is to be understood that the above description is merely illustrative of preferred embodiments of my invention ofwhich many variations may be made by those skilled in the art without departing from the spirit thereof.

I claim:

1. A process for dewaxing oils which comprises mixing waxy oil with a liquefied normally gaseous hydrocarbon'solvent, passing said mixture con-. tinuously in a vertical confined stream, vaporizing solvent from said mixture by lessening the hydrostatic head on said mixture to chill the oil and precipitate the wax, removing the vaporized solvent at a plurality of points in said stream and separating the precipitated wax from the oil and remaining solvent.

2. A process for dewaxing oils which comprises mixing waxy oil with a liquefied normally gaseous hydrocarbon solvent under pressure, passing said mixture through a plurality of chilling chambers from the bottom upwardly, maintaining the pressure at the top of said chilling chambers substantially the .same as the pressure at the bottom of the next succeeding chilling chamber, vaporizing solvent in said passage through said chilling hydrostatic head, ,removing vaporized solvent at a pluralitypf stages in said chilling chambers and separating precipitated wax from the'oil and remaining solvent.

3. An apparatus for separating wax from oils which comprises means for mixing waxy oilwith' a liquefied normally gaseous solvent, a plurality of vertical chillers, means for passing said 011- solvent mixture through said chillers in the direction of decreasing hydrostatic head, means in said chillers to collect solvent vaporized from said oil-solvent mixture by lessening of hydrostatic head, means for removing solvent from said vapor collecting means and means to con-.

means. a 4. An apparatus for separating wax-from oils which comprises means for mixing waxy oil with a liquefied normally gaseous solvent a plurality of chilling chambers, means for introducing said mixture into the bottom of the first or said chilling chambers,me'ans for passing said mixture from the top of each chilling chamber to the level in said vapor collecting bottom of succeeding chilling'chambers. a plurality of compartments in said chilling chambers "for trapping solvent vaporized from said oilsolvent mixture by lessening of hydrostatic head,

.means' to control the liquid level in said comcomprises a-di'aphragm connected to said valves I solvent. v r 5. An apparatus 'as in claim 4 in which the partments, means to maintain the pressure at the .top of said chilling chambers substantially equal to'the pressure at the bottom of the next succeeding chilling chambers and means'ior removing precipitated wax from the oil and remaining means for maintaining liquid level in said comcompartments:

partments comprises. a valve connected, to said means ior removing vapors from said -com1:iartments'and actuated'by the level of liquid in said ..-6. Anapparatus for separating wax'irom oil which comprises a plurality of chillers, conduits ments, means for controllingliquid level at a' whichcomprises a plurality passing waxy oil and solvent into. the bottom of connecting the top of each ,chiller "to'the bottom of succeeding chillers, means for introducing a mixture of waxy oil and liquefied normally ga eous solvent into the bottom of the first chiller,

a plurality'of compartments in each '01 said 4 chillersinto which solvent vaporized by lessening of the hydrostatic head is collected, means-"for removing vaporized solvent from-said compartpredetermined point-in said compartments, said means comprising a valve 'on said vapor removing means actuated bythe level of liquid in said comseparating wax from oil 'lessening of thehydrostatic head, means or removing said vaporized solvent from .said vapor trapping means whereby said oil and solvent may be chilled at a gradual controlled rate and with-' in the metastable range of supersaturation to precipitate wax in largecrys'tals and means .ior removing said precipitated wax from said 011 and remaining solvent. I

11. An apparatus Iorseparating wax from oil which comprises means for commingling wan oil with a liquefled'normally gaseous solvent, a

mixing'waxy oil withplurality of vertically. disposed chillers, means connecting said mixing'meanswlth the bottom oi the first of said chillers, means for passing partments, means for maintaining the pressure at the top of said chillers substantially the same as the pressure at the bottom of the next succeeding chiller, float control valves on the conduits connecting the top and bottom of the suc-.

ceedin'g chillers, said float control'valve being positioned at a point adjacent the bottom of said chillers and controlled by the liquid level atthe top or theznext preceding chiller, means for re moving oil, remaining solvent and precipitated wax from thetop of the last chiller and means separating the precipitated wax-irom the' oil and remaining'solvent. 1 7. Anapparatus forseparating wax from oil oi chillers, means for the first chiller, means 'for' passing oil and solvent from the top of said c hillers to the bottom of the next succeeding chillers, means for removing vaporized solvent by lessening of the hydrostatic head from said chillers, means for controlling the pressure at the top of said chillers substantially the same as the pressure at the bot- '8. An apparatus'ror separating wax tom oi the next succeeding. chillers, said means comprising a valve connected to said means for removing vaporized solvent from said chillers operated by a float control positioned removing chilled oil, solvent and wax from the topor said last chiller.

which comprises-a plurality of -.vertical chillers, means for introducing a, mixture, of waxyoil and liquefied normally gaseous solvent intothe bottom of the first chiller, means connecting the at. the bot- .tom of the next. succeeding chiller and means for precipitated from oil top of each chiller with the bottom or the next succeeding chiller, means for; removing solvent vaporized. by lessening oithe hydrostatic head from said chillers, means. on said vapor removing means for controlling the pressure in said chillers, said 'means comprising a valve actuated by the vapor pressure in sai d'chillers.

4 9. An apparatus as in 'claim 8 means for controlling the pressure in said chillers on said vaporized solvent removing means, said diaphragnr being actuated by the difierentlal pressure between adjacent chillers whereby the "pressure at the top'oi said chillers is controlled m'wmch e) -ated by'the said mixture. from the top to the bottom of succeedingrchillers, means within said chillers forcollecting' solventv vaporized from said mixture by lessening of hydrostatic head, means for main taining collecting means, said means comprising a valve on. said vapor. removing means actuated by the liquid level insaid vapor collecting means, means for'maintaining the-pressure at successive chillers substantially the same as the pressure at the' top of the preceding chillerssaid means -comprising 'a valve 'on said means for passing said mixture from one chiller to the next' and positioned at the bottom thereof andactuliquid level at the top of the next preceding chiller, means forremoving chilled oil,

a predetermined liquid level in said vapor the bottom of solvent and precipitated wax from the top oi the last chillerand means Io'r removing precipitated wax from the oil and solvent.

'12. A process for chilling liquids which com-' prises mixing the liquid with a volatile liquid under superatmosphe'ric pressure, maintaining a series oichilling columns with said mixture, in-- troducing the mixture into the first of said chilling'columns under a pressure substantially equal to the sum of the hydrostatic heads of liquid in said chilling columns and then passing the mixture through the columns in series relationships in the direction of decreasing hydrostatic head whereby a portion or the volatile liquid is gradually vaporized ,by the reduction in hydrostatic head and chilling of the mixture is accomplished, withdrawing vaporized volatile liquid. from the chilling columns and withdrawing chilled liquid from the last or said chilling columns.

13. A process for chilling liquids which comprises mixing the liquid to be chilled with a volatile liquidrefrigerant under superatznos'pheric pressure, maintaining a column of the-mixture of liquid refrigerant and liquid to be chilled in a chilling column, introducing the mixture to be chilled into the bottom of the chilling column under a pressure substantially equal to the hydro static head ofmixture in the chilling column plus the vapor'pressure of the said chilling column, chilling themixture in said chilling column by reduction in hydrbsta tic head as itfflows upwardly in said column, withdrawing vaporized refrigerant from the chilling col-- umn resulting from said release in pressure and withdrawing chilled from the column at mixtureatthetopof.

a point above the point of introduction of said mixture into said chilling column.

14 A process as in claim 13 in which the vaporized liquid refrigerant is-withdrawn from the chilling column at a plurality of points.

15. A process as in claim 13 in which the vaporiz'ation of the volatile liquid refrigerant in said chilling column is controlled at a plurality of points in said column. i

16. A process for chilling oils which comprises dissolving the oil in a volatile hydrocarbon diluent under superatmospherie pressure, maintaining a plurality of chilling columns of said mixture, said columns being connected'in series, introducing the mixture into the bottom of the first chilling column under a .pressure' substantially equal to the sum oi the hydrostatic headsof static head from said chilling columns.

17'. A process as in claim '16 in which the vapor pressure at the top ofsaid, chilling columns is controlled by the diiierential pressure betweenadjacent chilling columns to maintain the pres-- sure at the top of said chilling columns substantially equal with the pressureat the bottom of the next succeeding chilling columns.

18. A process ior-dewaxing oils which comprises mixing waxy oil with a volatile liquid refrigerant under superatmospheric pressure, maintaining a column of the mixture of liquid refrigerant andwaxy oil to be chilled in a chilling column, introtiming the mixture to be chilled into the bottom of the chilling column under a pressure substantially equal to the hydrostatic. head ofmixture inthe chilling column plus the vapor pressure of the mixture at the topof saidchilling column, chilling the mixture in said chilling column by reduction in hydrostatic head as it flows upwardly in said column .to precipitate wax in the oil and refrigerant, withdrawing vaporized refrigerant from the chilling column resulting from said re lease in pressure and withdrawingchilled oil, refrigerant and precipitated wax from said chill- -ing column at a point above the point 01 introduction of said mixture into said chilling column.

19. A processas in claim 18 in which the volatile liquid refrigerant eous hydrocarbon.

' 20. A process as in claim 18 in 'which the volatile liquidre'frigerant is liquid propane.

21. A process for separating wax from oil which comprises dissolving the waxy. oil 'in a liquefiednormally gaseous hydrocarbon under superatmospheric pressure, maintaining a series of chilling columns with said mixture, passing the mixture intothe first of said chilling columns in series under a pressure substantially equal to the sum Ba liquefied normally gasof the hydrostatic heads of liquid in said chilling columns, vaporizing diluent .from the mixture under controlled reduction in hydrostatic headoi' liquid in said columns to provide a uniform temperature gradient to chill the oil and diluent to a sufficiently low temperature to precipitate wax irpm the oil and diluent, controlling the pressure in-"'the upper portion of said chilling columns to correspond with the vapor' pressure in the upper portion of the next succeeding column plus the hydrostatic head of liquid in said column, withdrawing chilled oil'and diluent containing precipitated wax from the last of said chilling columnsand separating the precipitated wax from the oil and diluent.

22. The method of continuously chilling a mixture of a wax-bearing oil with a normally gaseous diluent to form filterable wax crystals, which comprises introducing said mixture at the base of a tower which is substantially filled with liq-1 uid, and slowly passing said mixture upwardly in said tower to gradually lower the hydrostatic pressure andpermit the gradual vaporization of diluent, withdrawing liberated gaseous diluent to prevent turbulence and gas-lift eil'ects, and continuously decreasing the hydrostatic headuntil dewaxing temperature is reached.

23. -A continuous chilling tower for use in a propane 'dewaxing process which comprises a tower,

means for introducing a propane waxy ofl mixture at the base of the tower and for withdrawing the propane waxy oil mixture from the top 01' the tower and a plurality o1 propane trapoutsvertically spaced along the side of said tower,

- each or said trap-outs containing means for preventing the escape of liquid with vaporized propane. I

DAVID R. 

